European Patent Application 488 719 A2 describes a device and a method of detecting partial discharges in gas-insulated high voltage facilities (see FIG. 6 there), where a fundamental frequency and an HF component below a few hundred kHz, possibly generated by interference, are picked up. These signal components can be separated using filter devices. The signals thus obtained are converted to a form suitable for further processing by using filter devices and sent to a computer system. The signal obtained in the high frequency range below a few hundred kHz is used to identify external interference. The zero crossing of the high voltage acts as a trigger signal for the start of the partial discharge measurement. Partial discharge signals in the range of a few 10 MHz are recorded by a second sensor and processed further in a suitable signal processing branch for identification of the partial discharges. With the wiring described there, this sensor is operated at a few 10 MHz in antenna mode and thus cannot be calibrated for partial discharge measurements.
In this connection, the HF range should be understood to be the frequency range between a few 10 kHz and 100 MHz and the UHF range should be understood to be the frequency range above 100 MHz.
German Patent Application 195 48 466 A1 describes a device the gate is blocked when there is a measurement signal from a sensor, with the input signal for controlling the gate being an HF (High Frequency) signal below 10 MHZ, for example. The signal allowed through by the gate for further processing may be a broad-band UHF signal in the range up to 1.5 GHz, for example. In this way, interference in measurement of partial discharges is to be avoided. However, no calibrated measurement is provided with this system.